The present invention relates to novel bisazo compounds represented by the general formula. ##STR2## wherein R represents a halogen selected from the group consisting of fluorine, chlorine, bromine and iodine, and when R is fluorine, it is at the ortho, para or meta position in each phenylcarbamoyl group; when R is chlorine, it is at the ortho positions; when R is bromine, it is positioned at the ortho or meta positions; and when R is iodine, it is at the meta positions.
Conventionally, some of bisazo compounds have been found to be useful as charge generating pigments for use in a charge generating layer of a layered electrophotographic photoconductor. The layered electrophotographic photoconductor comprises an electrically conductive base, a charge generating layer formed on the electrically conductive base, and a charge transporting layer formed on the charge generating layer.
Generally, the charge generating layer is formed on the electrically conductive base by vacuum evaporation onto the electrically conductive base of a pigment capable of generating charge carriers upon impigement of light thereon, or by coating on the electrically conductive base a resinous liquid in which fine particles of such a pigment are dispersed. The charge transporting layer is usually made of a charge transporting material and a binder resin for holding the particles of the charge transporting material, and is capable of transporting charge carriers injected from the charge generating layer in the desired direction.
As bisazo pigments employed in a electrophotographic photoconductor of the above described type, bendizine-type bisazo compounds disclosed in U.S. Pat. No. 3,898,084 and U.S. Pat. No. 4,052,210, and fluorenone-type bisazo compounds disclosed in Japanese Laid-open patent application Ser. No. 54-22834 are known. Other bisazo pigments for use in an electrophotographic photoconductor are disclosed in U.S. Pat. No. 4,242,260.
However, the conventional layered electrophotographic organic photoconductors employing those bisazo compounds are low in photosensitivity in comparison with the conventional electrophotographic inorganic photoconductors employing selenium-arsenic alloys, for example, As.sub.2 Se.sub.3 and therefore are not suitable for use in high speed copying.